1. Field of the Invention
The present invention relates to a multilayer ceramic capacitor, and relates particularly to a multilayer ceramic capacitor including an external electrode including a multilayer structure.
2. Description of the Related Art
In recent years, multilayer ceramic capacitors have been used under a severe environment more susceptible to an impact than the prior art, so that the multilayer ceramic capacitors are required to have mechanical strength that can correspond to this. For example, multilayer ceramic capacitors for use in mobile devices such as cellular phones and portable music players are required to withstand impact such as dropping. Specifically, the multilayer ceramic capacitors are required to keep from dropping from mounting boards and keep themselves from being cracked, even when subjected to impact such as dropping. In addition, multilayer ceramic capacitors for use in vehicle-mounted devices such as ECU are required to withstand impact such as thermal cycling. Specifically, the multilayer ceramic capacitors are required to avoid being cracked even when subjected to deflection stress generated by linear expansion and contraction of the mounting boards in thermal cycling and a tensile stress applied to an external electrode.
For the purpose of responding to requirements as described above, a multilayer ceramic capacitor provided with an external electrode including a thermosetting resin layer is known. Japanese Patent Application Laid-Open No. 11-162771 discloses such a multilayer ceramic capacitor.
The multilayer ceramic capacitor of Japanese Patent Application Laid-Open No. 11-162771 is provided with an external electrode having a multilayer structure including electrode layers as baked electrodes formed on both end surfaces of a capacitor body and a conductive thermosetting resin layer formed on a surface of the electrode layer. In the multilayer ceramic capacitor of Japanese Patent Application Laid-Open No. 11-162771, the electrode layer has a function of ensuring moisture resistance reliability in the external electrode having the multilayer structure, and the thermosetting resin layer has a crack prevention function to the capacitor body.
Since a multilayer ceramic capacitor as disclosed in Japanese Patent Application Laid-Open No. 11-162771 contains a resin in the thermosetting resin layer, the content of a metal contained in the thermosetting resin layer is low. Thus, an adhesive force between the thermosetting resin layer and an electrode layer formed on a lower surface of the thermosetting resin layer tends to be weak. Consequently, the multilayer ceramic capacitor as disclosed in Japanese Patent Application Laid-Open No. 11-162771 has a problem that moisture or the like intrudes between the thermosetting resin layer and the electrode layer, and moisture resistance reliability and electrical characteristics are deteriorated.
As a method for solving the above problem, a measure exists to form an alloy layer between the electrode layer and the thermosetting resin layer. However, there has been a problem that if the amount of alloy between the electrode layer and the thermosetting resin layer is too large, a crack prevention function due to the thermosetting resin layer is deteriorated.